Vagus Nerve
On this page
Direct answer
The vagus wanders further than any cranial nerve — from four medullary nuclei through the jugular foramen, down the neck in the carotid sheath, through the thorax and into the abdomen as far as the left colic flexure. Its dorsal motor nucleus supplies parasympathetic fibres to thoracic and abdominal viscera, the nucleus ambiguus supplies the striated muscles of palate, pharynx and larynx, the solitary nucleus receives taste from the epiglottic region and visceral afferents, and the spinal trigeminal nucleus receives sensation from part of the external ear. The recurrent laryngeal nerves — right around the subclavian artery, left around the aortic arch — supply all intrinsic laryngeal muscles except the cricothyroid and sensation below the vocal folds.
What you must remember
- Nuclei: dorsal motor nucleus (parasympathetic, gut as far as the left colic flexure), nucleus ambiguus (branchial motor: palate except tensor veli palatini, pharynx except stylopharyngeus, all laryngeal muscles), solitary nucleus (taste, epiglottis; visceral afferents from aortic body and thoraco-abdominal organs), spinal trigeminal nucleus (skin of the concha and small part of the external meatus — Arnold's auricular branch).
- Course: leaves the retro-olivary sulcus, exits the jugular foramen with the accessory nerve, bears its superior (jugular) and inferior (nodose) ganglia, then runs within the carotid sheath between and posterior to the internal jugular vein and internal carotid (then common carotid) artery.
- Neck branches: pharyngeal branches to the pharyngeal plexus (the motor route of the gag reflex), superior laryngeal nerve — internal laryngeal (sensory above the vocal folds) and external laryngeal (motor to cricothyroid), cardiac branches, and the auricular branch.
- Recurrent laryngeal nerves: the right hooks around the right subclavian artery, the left around the aortic arch below the ligamentum arteriosum — both ascend in the tracheo-oesophageal groove to enter the larynx.
- Hoarseness anatomy: external laryngeal nerve injury (thyroid surgery) weakens the voice with loss of high pitch; unilateral recurrent laryngeal injury gives hoarseness and a bovine cough; bilateral injury causes stridor with adducted cords.
- Abdominal destination: through the oesophageal hiatus, the anterior and posterior vagal trunks distribute to the stomach and, via the coeliac and superior mesenteric plexuses, to the gut up to the left colic flexure — the midgut endpoint that the distal colon and pelvic organs outsource to the pelvic splanchnic nerves (S2–S4).
- High lesion signs: ipsilateral palatal droop with uvula deviating away from the lesion, nasal regurgitation, dysphagia, hoarseness, loss of gag efferent — the neurologist's "first-year syndrome" of the jugular foramen neighbourhood.
- Referred pain: vagal afferents from the larynx and heart project to the brainstem but are felt in the ear (Arnold's branch overlap) — laryngeal and oesophageal disease presenting as ear pain.
Localising a hoarse voice step by step
A man develops hoarseness; work from the vocal fold backwards. Direct laryngoscopy shows the left cord paralysed in the paramedian position — a left recurrent laryngeal palsy until excluded. The left nerve's long thoracic detour makes it a spectator of disease: an apical lung tumour, an enlarged mediastinal lymph node, an aortic arch aneurysm or an enlarged left atrium can each strangle it, which is why a smoker with new hoarseness and a normal cord on inspection needs a chest radiograph. If the cord lies flaccid and cadaveric in abduction instead, the lesion is higher — the recurrent laryngeal fibres have been joined by the external laryngeal and pharyngeal branches, placing the injury at or above the nodose ganglion. Add a drooped soft palate, weak gag and displaced uvula on the same side, and the lesion sits at the jugular foramen — with the eleventh nerve's shoulder weakness completing Vernet's syndrome. Finally, separate the nucleus from the nerve: in lateral medullary infarction the nucleus ambiguus is struck, giving hoarseness and dysphagia with the vertebral artery territory signs — vertigo, crossed sensory loss and ipsilateral Horner syndrome — that make Wallenberg's syndrome the composite viva answer.
Where students slip
The boundary of vagal parasympathetic supply — to the left colic flexure (of Cannon and Böhm) — is mis-quoted as "the whole gut" or "the stomach"; the distal colon and pelvic organs belong to S2–S4. The second slip is the recurrent laryngeal nerve's muscles: all intrinsic laryngeal muscles except cricothyroid, and sensory below the cords, while the internal laryngeal covers sensation above — candidates swap them. A non-recurrent right laryngeal nerve, passing directly from the vagus to the larynx when the right subclavian artery arises aberrantly from the descending aorta, is the celebrated anatomical trap that endangers thyroid surgeons and decorates postgraduate papers.
Frequently asked questions
Which four nuclei contribute fibres to the vagus nerve?
The dorsal motor nucleus (parasympathetic to viscera), nucleus ambiguus (motor to palate, pharynx and larynx), solitary nucleus (taste from the epiglottic area and visceral afferents) and the spinal trigeminal nucleus (sensation from part of the ear). This makes the vagus the most pluripotent of cranial nerves.
Why does the left recurrent laryngeal nerve have a different course from the right?
Embryologically each nerve hooks under the sixth aortic arch artery. On the left the ductus arteriosus (ligamentum arteriosum) retains the anchor at the aortic arch; on the right the distal vessel is absorbed, leaving the nerve to hook around the right subclavian artery.
What are the effects of unilateral vagal injury above the nodose ganglion?
Ipsilateral palatal paralysis with uvular deviation away from the lesion, nasal regurgitation, dysphagia, hoarseness from cord paralysis and loss of the gag efferent. Companion ninth and eleventh nerve signs localise the lesion to the jugular foramen.
How far does vagal parasympathetic supply extend in the abdomen?
To the midgut and hindgut as far as the left colic flexure, distributed through the coeliac and superior mesenteric plexuses. The distal colon and pelvic viscera receive parasympathetic supply from the pelvic splanchnic nerves S2–S4.
Why can laryngeal or oesophageal disease cause ear pain?
The auricular branch of the vagus (Arnold's nerve) supplies the concha and part of the external meatus, and its ganglion shares brainstem relays with visceral afferents. Irritation of vagal territory below is therefore referred to the ear.